Damping system for measuring devices



July 23,1940.

R. ROWELL I DAMPING SYSTEM FOR MEASURINQ DEVICES Filed May 5, 1939 Fig.4. 22

Inventor- Ralph M Rowell 'byfl 6.1

V Z\I IIIIIIII H is Attorney Patented July 23, 1940 UNITED STATESDAMPING SYSTEM FOR. MEASURING DEVICES I Ralph M. Rowell, Lynn, Masa,assignor to General Electric Company, a corporation of New YorkApplication May 5, 1939, Serial No. 271,949

4 Claims.

My invention relates to indicating instruments and concerns particularlydamping arrangements for deflecting measuring instruments of the longrange type.

It is an object of my invention to provide an improved, eflicient,light, and compact damping arrangement for instruments which haverelatively rotatable parts designed for rotation through a largefraction of a complete revolution or for rotation through a plurality ofrevolutions. Other and further objects and advantages will becomeapparent as the description proceeds.

In carrying out my invention in its preferred form in connection with a250 degree deflecting pointer type measuring instrument, for example, Iprovide a light damping vane of current-conducting material, which isarcuate in shape and concentric with the axis of revolution of themovable element of the instrument, and a damping field-producing memberincluding a soft iron ring-shaped keeper member and a plurality ofbutton type permanent magnets composed of high-coercive-forcepermanent-magnet material spaced from the keeper member to form air gapsthrough which the vane travels as the movin element of the instrumentdeflects.

The invention may be understood more readily from the following detaileddescription when considered in connection with the accompanying drawingand those features of the invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. In thedrawing Figure 1 is a side elevation of an electrical instrumentembodying my invention having a portion thereof cut away to expose avertical section through the instrument. Figure 2 is a front elevationof the damping system shown in the instrument of Figure 1. Figure 3 is abottom plan view of the apparatus of Figure 2. Figure 4 is a crosssection through the apparatus of Figure 2 cut by the plane 4-4. Figure 5is a perspective view of one of the button magnets utilized in theapparatus of the precedin figures and Figure 6 is a diagrammaticperspective view of an arrangement for magnetizing the button magnets.Like reference characters are utilized throughout the drawing todesignate like parts.

In Figure l a damping arrangement constructed in accordance with myinvention is illustrated in connection with a long scale wattmeterdesigned for an, angular length of scale of 250 degrees or more. Thewattmeter comprises a magnetic field system H composed! of laminatedmagnetizable material, a stationary field coil l2, a rotatableeccentricallyimounted coil l3 carried by a rotatable shaft ll, a pointerl5 also'carrled by the shaft l4 cooperating with a scale, not shown, adamping system It, and a frame 41 for supporting the parts of theinstrument, all mounted within a suitable casing is.

The damping system l6 includes a damping field-producing member l6 shownmore clearly in Figures 2 and 3 and a damping vane IS. The dampingfield-producing member l6 comprises a substantially ring-shaped keepermember composed of a. relatively permeable magnetic material, such assoft iron or punched steel, for example, a plurality of button typepermanent magnets 2| and a substantially ring-shaped magnet holdingmember 22. The keeper member 20 and the holding member 22 need not becomplete rings. For example, there may be a break 23 in the keepermember 20 and the magnet holding member 22 may, if desired, be in twoparts having breaks at 23 and 24. For the purpose of securing the magnetholding member 22 to the keeper member 20 and supporting them, they maybe provided with radially projecting cars 25 having openings therein forbolting the damping fieldproducing member it to a suitable stationarypart of the apparatus, such as the posts 26 shown in Figure 1. Thebutton type magnets 2! are so mounted in the magnet holding member 22 asto be radially spaced from the magnet keeper member 29 to leave air gaps2i through which the damping vane i9 may travel as the movable coil itof the instrument deflects. The damping vane it is secured to the shaftM and is preferably composed of some relatively light, buthigh-conductivity current-conducting material, such as aluminum, forexample.

The damping field-producing member it and the damping vane l9 areconcentric with the instrument shaft i l. The button magnets 2! aremounted around the periphery of a circle having .a radius the same asthe mean radius of the arcuate damping vane I9 so that the damping vaneis under the influence of the magnetic field of some of the buttonmagnets regardless of its angular position. Preferably the buttonmagnets are spaced at substantially equal intervals around the peripheryof the circle and the angular length of the damping vane I9 is made notless than substantially twice the angular spacing interval of the buttonmagnets in order that the damping vane will always be in the field of atleast two button magnets and the damping effect will be substantiallyuniform.

The magnet holding member 22 is composed of any suitable nonmagneticmaterial, for example, a die casting alloy. Accordingly when forming themagnet holding member 22 the button magnets 2l may be mounted in themold as inserts so that they will be held in position by the die castingoperation. I

The button magnets Hate preferably com-- posed of a high-coercive-foroepermanent-map cilanet material such as the material describm, forexample, in United States Patent 1,968,569 Harder and I have obtainedsatisfactory results with alloys composed of from 17 to 20% nickel, 55to 63% iron, 10 to 12% aluminum and up to 12% cobalt. The button typemagnets 2i consist or small flat cylinders or buttons with a etricalnotch 28 cut in one face thereof (Figure 5) The buttons are somagnetized that the portions of the slotted base of the cylinder oneither side of slot 28 form pole faces 29 and 3d of opposite polarity.It will be observed from Figure 3. that,

in die casting the button into the magnet holding member 22, a portionof the die cast material it is caused to How around the base of the slot23 in order to form a secure and rigid holding structure for the buttonmagnet it. It will be understood that the distance across the notch 25from poleto pole is to be no less than twice the length of the air gap2? in order to avoid excessive leakage flux. I have obtainedsatisfactory results by making the air gap inch and the distance betweenpole faces across the notchinch. The button magnets may be regarded asU-type magnets as distinguished from bar magnets for the reason thatthey have their pole faces in relatively close proximity and in the sameplane I a.

The button magnets 2!! may be magnetized in any desired manner, but itwill be understood that owing to their high-coerciveiorce a highmagnetizing force will be required. For example, if desired, two buttonsto be magnetized may be placed on either side of a current conductingbar 32 of such size as to fit into the magnet slots 28 and to allow thepole faces of the two button magnets to abut. A very heavy directcurrent is then passed through the bar 32 by means of any suitablehigh-current low-voltage source.

such as a welding generator, for example.

In order that the damping vane it maybe caused to have its leading end33 pass under the influence of one'pf the poles of one of the buttonmagnets simultaneously with the trailing end 35 of the vane passing awayfrom one of the poles of another of the button type magnets, the arcuatelength of the vane as may be made an even multiple of the arcuatespacing between the centers of the buttonv magnets, and the buttonmagnetsmay be mounted with their slots 28 re.- dial so that the centersof the pole faces all lie in the same circle and have the same radius asthe average radius of the vane it. Preferably the angular length of.thedamping vane I9 is not less than substantially twice the angular spacingbetween the button magnets 29.

It will be understood by those skilled in the art that damping of themotion of the movable element of the instrument takes place in a mannercommon to electromagnetically damped instruments. The flux from eachbutton magnet reaches across the air gap to the soft iron keeper 20.Since each of the individual button magnets has two pole face'stheflux-from the north pole will bridge the gap to the keeper member andthence return across the second'gap from' the keeper member to the southpole. The flux is intercepted by the motion of the vane 19 which isattached to the movable element and eddy ourrents are setup in the vanein such a direction as to oppose the motion oi the movable element.

In accordance with the pr one of the patent statutes, I have descri thepciple of operaeoaase ation of invention together with the apparatuswhich I now consider to represent the best embodiment thereof but Idesire to have it understood that the apparatus shown is only illustra-,

tive and that the invention may be carried out by other means' at Iclaim as new and desire to secure by Letters Patent of the United Statesis:

1. A damping system for long range deflecting instruments havingrelatively rotatable elements, comprising in combination an arc-shadamp= ing vane concentric with the axis of relative rotation of theinstrument elements composed of rel= atively light current-conductingmaterial secured to one of said elements, and a magnetic heldproducingmember secured to the other of said elements, said latter membercomprising asub-= stantially ring-shaped keeper member composed ofmagnetizable material, amagnet holding meru= ber composed oi nonmagneticmaterial and a plu= rality of button type permanent magnets composed ofhigh-coercive-force material moun in said magnet holding member aroundthe pe= riphery of a circle with their pole faces axially spaced fromsaid keeper member to form gaps including the path of said vane and withtheir pole centers at substantially equal radial distances from. theaxis of relative rotation, the angular length of said damping vane beingnot less than substantially twice the anar spacing between said buttonmagnets.

2. A damping system for long range deflec instruments having relaitvelyrotatable elements, comprising in combination a damping vane composed ofcurrent-conducting material secured to one of said elements and amagnetic field-pro.-

ducing member secured to the other of said elements, said latter membercomprising a substan= tially ring-shaped keeper member composed ofmagnetizable material, and a plurality. of button type permanent magnetscomposed of high-coeroive: force permanent-magnetmaterial mounted aroundthe periphery of a circle, each such net having a plurality of polefaces ay spaced from said keeper member to form air gaps including thepath of said vane.

3. A damping system for an instrument having relatively rotatableelements comprising a ing vane composed of current-conducting rialsecured to one of said elements and a mag= netic field-producing membersecured to the other of said elements, said latter member comprisinga'substantially ring-shaped keeper mem= ber composed of magnetizable'material, and a plurality of closely spaced U-type g- 1' magnets eachhaving a pair of pole faces :a w from said keeper member to form airgaps, each including the path of said vane.

4. A damping system for a current responsive device having relativelyrotatable elements comprising a damping member composed ofcurrentconducting material secured to one or said elements and amagnetic field-producing member

